This invention relates to waveguide cavity filters for use in radio communications systems and, in particular, to waveguide cavity filters disposed in a triplet configuration for implementing a bandpass filter.
As demonstrated by the high prices paid for licenses to portions of the radio frequency spectrum in the United States, there is a need to maximize the services that can be provided over a limited bandwidth. This need is particularly critical in the field of cellular phone communication systems.
Waveguides may be employed in communication systems to minimize losses for high frequency radio waves. Conventionally, waveguide bandpass filters include one or more resonance cavities and coupling probes disposed between each cavity. The use of probes is disadvantageous because the placement of probes is often unpredictable, unrepeatable, and costly. Accordingly, highly efficient waveguide bandpass filters that minimize or eliminate the use of probes have been difficult to achieve.
Objects of one or more aspects of the invention include overcoming the above problems and disadvantages to form a highly efficient waveguide filter trisection; locating transmission zeros on only one side a filter passband; and providing a bandpass filter without the use of probes to capacitive coupling adjacent waveguide cavities. One or more of these above objects may be achieved by various aspects of the present invention.
In one aspect of the invention, high-dielectric materials are used in waveguide cavities in a triplet or tri-section configuration to produce transmission zeros on only one side of the filter passband.
In another aspect of the invention, the bandpass filter includes three waveguide cavities. Each waveguide cavity has a high-dielectric resonator positioned within the cavity. Windows are positioned between each adjacent pair of waveguide cavities to inductively couple the cavities. Signals introduced into the cavities are filtered by the interaction of the cavities within the tri-section. The arrangement of the coupling apertures between each adjacent pair of waveguide cavities contributes to the filtering function and causes the transmission zeros to occur at predetermined frequencies on one side of the filter passband.
In still further aspects of the invention, the filter may include three waveguide cavities connected in a tri-section configuration. Where two apertures and one probe are utilized to couple the tri-section, transmission zeros appear only on the high side of the passband. Where three apertures are utilized to couple the tri-section, the transmission zeros appear only on the low side of the passband.
In yet other aspects of the invention, the filter may include two, three, four, five, six, or more tri-sections coupled together. In these configurations, the filter may provide transmission zeros on one or both sides of the passband.
In still other aspects of the invention, the filter may include first, second, third, fourth and fifth waveguide cavities with the first, second, and third waveguide cavities being coupled together in a first tri-section configuration, and the third, fourth, and fifth waveguide cavities being coupled together in a second tri-section configuration. In some aspects of the invention, first, second, third, fourth, and fifth coupling apertures are respectively disposed between the first and second, the second and third, the third and fourth, the fourth and fifth and the third and fifth waveguide cavities.
The invention may also include a method of filtering which uses a first waveguide cavity tri-section to bandpass filter a signal by passing the signal in a passband while producing transmission zeros only on one side of the passband.
These and other objects and features of the invention will be apparent upon consideration of the following detailed description of preferred embodiments thereof, presented in connection with the following drawings in which like reference numerals identify like elements throughout. Although the invention has been defined using the appended claims, these claims are exemplary in that the invention is meant to include the elements and steps described herein in any combination or subcombination. Accordingly, there are any number of alternative combinations for defining the invention, which incorporate one or more elements from the existing claims and/or specification (including the drawings) in various combinations or subcombinations.